Hi Bud,
I did a quick search for the optimal operating points for the 6SL7/12SL7 and according to kevinkr it is best at 1.5-2ma.
Here's another interesting 6SL7/12SL7 thread.
Let's take 1.8ma with a lowish 240v B+, to get 1.8ma you need to adjust the resistor of the LM334.
The 82K for the plate is a guess: Broskie uses 120K for the 12AX7, the 6SL7 has 2/3 of the internal resistance of a 12AX7, so 2/3 of 120k is about 82k.

The best way for finding the resistor values for the operating points is to simulate it with a Spice program like LtSpice, install the spice models, start from an existing spice tube circuit and adjust it to the Broskie Unbalancer.

Is anyone finding that V1/V2 and V3/V4 are getting slightly different filament voltages?

eg. on V1 and V2 (both 6n23p) I read 6.12v on V1 and 6.42v on V2. The plate/cathode readings also differ: 132.3v on V1 and 134.8 on V2.

I'd have thought each tube should be identical?
I have similar problems on V3 and V4.

On another note, normally to look at plate curves we can measure the voltage across the cathode resistor, then also take the plate voltage. This is ok for V3 and V4 (eg. I get 120v on the plates and 2.5v across the cathode resistors R13 and R14), however how do we take these measurements for V1 and V2 given there is a LM334 controlling the situation?